In silica-loaded tires, bis-triethoxysilyltetrasulfide is widely used as a coupling agent between rubber and silica. However, when mixed with rubber and silica at elevated temperatures, this compound acts to increase the viscosity of the blend, which is inconvenient to subsequent operation.
To overcome this problem, shorter chain polysulfide compounds such as bis-triethoxysilylpropyldisulfide were proposed. For example, JP-A 9-169774 discloses a method for preparing disulfide silanes using NaCN. This method, however, has the problem of using the toxic compound. It would be desirable to have a substitute safe method of preparing short sulfide chain-bearing organosilicon compounds at low cost.
The inventors proposed in JP-A 11-100388 a method of preparing a short sulfide chain-bearing organosilicon compound by reacting a polysulfide silane of the general formula: (RO)3SiC3H6SxC3H6Si(OR)3 wherein R is methyl or ethyl, and x is a positive number of 3 to 6 on the average, at least one anhydrous sulfur compound: M12S or M2S wherein M1 is an alkali metal or ammonium and M2 is an alkaline earth metal or zinc, and a halogenoalkoxysilane of the general formula: XC3H6Si(OR)3 wherein X is halogen and R is methyl or ethyl. When the short sulfide chain-bearing organosilicon compound is prepared by this method, however, there can also be produced a monosulfide chain-bearing organosilicon compound, that is, an organosilicon compound having a sulfide chain which does not fully participate in the reactions with silica and rubber.